Interpretive Summary: Toxoplasma gondii is a single-celled parasite of all warm-blooded hosts worldwide. It causes mental retardation and loss of vision in children, and abortion in livestock. Cats are the main reservoir of T. gondii because they are the only hosts that can excrete the resistant stage (oocyst) of the parasite in the feces. Humans become infected by eating under cooked meat from infected animals, as well as food and water contaminated with oocysts. Here, the authors report fatal toxoplasmosis in manatees. Toxoplasmosis in marine mammals indicates contamination of marine waters with oocysts. The results will be of interest to biologists, parasitologists, and public health workers.

Technical Abstract:
Necropsies were conducted on four Antillean manatees (Trichechus manatus manatus) that were stranded in single events on the coastal beaches of Puerto Rico from August 2010-August 2011. Three manatees were emaciated and the gastrointestinal tracts were devoid of digesta. Microscopically, all manatees had severe widespread inflammatory lesions of the gastrointestinal tract and heart with intralesional tachyzoites consistent with Toxoplasma gondii identified by histological, ultrastructural and immunohistochemical techniques. The gastrointestinal lesions included severe, multifocal to diffuse, chronic-active enteritis, colitis and/or gastritis often with associated ulceration, necrosis, and hemorrhage. Enteric leiomyositis was severe and locally extensive in all cases and associated with the most frequently observed intralesional protozoans. Moderate to severe, multifocal, chronic to chronic-active, necrotizing myocarditis was also present in all cases. Additionally, less consistent inflammatory lesions occurred in the liver, lung, and a mesenteric lymph node and were associated with lesser numbers of similar tachyzoites. Sera (n=30) collected from free-ranging and captive Puerto Rican manatees and a rehabilitated/released Puerto Rican manatee from 2003-2012 were tested for antibodies for T. gondii. A positive T. gondii antibody titer was found in one (3%) of the free-ranging cases from 2004. Clinical disease caused by T. gondii is a rare disease in manatees. This is the first report of clinical toxoplasmosis in Antillean manatees from Puerto Rico. Additionally, these are the first reported cases of disseminated toxoplasmosis in any Sirenian. The documentation of four cases of toxoplasmosis within one year and the extremely low seroprevalence to T. gondii suggest that toxoplasmosis may be an emerging disease in Antillean manatees from Puerto Rico.